This invention relates to cannula insertion and to the exposure of, and to the subsequent protected relationship of, and following separation of, a stylet from a catheter.
The combination of a stylet and catheter for cannula insertion is well known as a "Catheter Placement Unit", and requires certain procedures and precautions in order to ensure communication into the intravascular space without puncturing the opposite wall of the blood vessel. The stylet functions to puncture the skin, subcutaneous tissue and blood vessel, when the catheter is retracted from the point of the stylet. The catheter is a tubular sleeve slidably engaged over the stylet to protect and reinforce the same, normally retracted a sufficient distance to expose only the truncated point of the tubular stylet. The catheter interior closely fits the stylet exterior, and its distal portion is conically tapered, for ease of entry into the punctured opening established by the stylet. It is for this purpose that the skin of the patient is tensioned through traction by one hand of the operator to prevent tissue and vessel displacement when the catheter placement unit is introduced.
Insertion of the catheter placement unit is to be executed by one hand of the operator, who advances the exposed point of the stylet through the skin and tissue and into the lumen of the vessel to be communicated with. During this step of the procedure, the flashback chamber of the stylet hub must be observed for filling with blood which indicates that the stylet point has entered the intravascular space, from which position the point may be moved ahead slightly but not to puncture the opposite wall of the vessel. It is from this condition that the catheter is to be advanced to cover the stylet coextensively, thereby to assure obscurity of the point thereof.
Following the aformentioned step of cannula insertion, the catheter must be advanced sufficiently to ensure reliable intravascular communication. This is safely achieved only when the point of the stylet is faithfully covered by the catheter tube, it being an object of this invention to ensure this protection by mechanical means having a definite and positive rule of action. Heretofore, such devices have not been infalible, and on the contrary have been entirely dependent upon the expertise of the operator and his best judgement as to position of the stylet point as related to the surrounding catheter tube. With the present invention this positioned relationship is accurately predetermined by a lever means.
Subsequent to the reliable insertion of the catheter tube to the desired depth of penetration, the stylet is withdrawn from the catheter and its hub and is disposed of, as it is an expendable item. The catheter is then ready for intravenous connection as circumstances require, it being an object of this invention to provide for the complete removal of the stylet and its hub and related features such as an air bleed plug and the like, and including the lever feature which characterizes this invention.
The foregoing catheter or insertion proceedure has depended greatly upon the expertise of the operator and his dexterity, and the highly skilled operator can complete the process only with difficulty; others often resort to freeing the first mentioned "one hand" from its traction capability, thereby subjecting the process to elastic recoil of the skin and likely displacement of the stylet the intravascular space often resulting in failure to properly place the catheter. It is an object of this invention to provide means by which one hand of the operator is reserved to the application of traction, and the other hand of the operator is reserved to operation of the catheter placement unit. With the present invention, the catheter placement and lever unit is manipulatable by the said single other hand of the operator.
There have been attempts at complex spring loaded trigger actuated devices for cannula insertion, but with traumatizing results and hazards. Such devices have therefore been unsuccessful, since a discrete and sensible application of such devices is not attainable. Accordingly, it is an object of this invention to provide means by which the operator can sense the position of the stylet catheter, and so that he can sensibly operate the lever means provided herein to effect a predetermined and positive correlationship of the catheter and stylet, and so that a tear or rupture of the vessel wall is precluded.
A functional requirement of the operator is to know of the rotative orientation of the stylet point truncation. That is, it is usually preferred that the truncation plane of the stylet point be faced upwardly; and that disposition can be related to the rotative position of features on the hub of the stylet. Accordingly, it is an object of this invention to position the lever means with respect to the position of said truncation. This angular displacement is preferably 90.degree., in order to realize a further objective of providing visual contact with the flashback chamber of the stylet hub. As a result, whether manipulated right or left handedly, the flashback chamber is always visible to the operator, since the lever operates in a plane 90.degree. to plane of truncation facing the operator. In practice, the lever is disposed to the right of the truncation plane for right handed operation. Left handed operators have two alternatives, one to employ the unit as disposed for a right handed person, and the other to revolve the unit 180.degree. so that the truncation plane is reversed. In either case, the flash chamber is visibly exposed.
The prior art has provided means for the expert operator to position the catheter to the stylet according to his best judgement, but not measurable to an exact relationship. In other words, no positive placement has been provided for, in which case the relative positions of the catheter and stylet have been conjecture and debatable, as a matter of fact in each instance of application. Therefore, it is an object of this invention to make the catheter and stylet relationship known in each instance, and particularly during deep penetration of the catheter into the intravascular space.
With the present invention, the catheter hub is freely rotatable, there are no extra devices connected to the catheter per se, and there are no disadvantageous modifications to the stylet and its flashback chamber and/or bleed plug. The lever system which characterizes this invention does not obstruct the flashback chamber, and does not encumber the catheter placement unit as such. It is by a simple pivot means that the lever means is attached to the stylet hub, and through this installation the catheter is positively shifted from an initial position where the stylet point is exposed, to a protective position where the stylet point is withdrawn and obscured.